The search for overlap.

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Re: The search for overlap.

Postby Fat Freddy » Sat Apr 25, 2015 7:41 am

PART II

Disclaimer - These are only my thoughts and I may have missed some obvious thing (not unusual for me) out so if I have omitted anything let me know.

A phrase that comes to mind is "One can't see the wood for the tree's". It fit's the search for overlap very well. Some say they can find it, some, like myself, struggle. But ironically almost all of us are wrong - in my mind. Most of those who say they can see it, can't. And those who say they can't see it, can. Make sense? Read on.

A couple of points I'd like to address. First of all I have to apologies for taking so long. TBH when I started the thread I thought I had the answer, it was in the bag. Then doing a couple of final checks I decided to compare the WPS actual pressure to the FLS output. And that was when I had to re-evaluate everything I had done. Make sure I hadn't created an element of the waveform (venturi effect for example). The head gasket popping also added some time. I had to make some new and improved fittings. And on top of that 'modify' the wife's car.
Which brings me to my second point. I would like to give a special mention to my wife for letting me attack/modify her car (mainly with a drill) all in the name of science. So thank you Mrs Fat Freddy for letting me improve your car.............. Steve S made me do it". :wink:


Let me begin:
Now I want to take you on an incredible journey. Not quite 'Alice down the rabbit hole' type. More of a 'Stan the spanner down the old exhaust pipe' type journey.

This first capture is one of the WPS in cyl 1 and the crank sensor. This is so I can see what events happen at a particular time on the clock/crank. I'm using this to indicate what specifically happens at particular times during the crank rotation. On the image I have marked out when an exhaust valve is open for each cylinder and also when exhaust valve overlap occurs. I have also marked out in blue (as best I can without specs) when the inlet valve is open at the same time an exhaust valve is - the overlap we are hunting for.
For each subsequent capture I have the crank sensor included so I can time the new capture with this following one. Also I will be syncing number 1 in the cycle by using the secondary ignition for cyl 1

image 1.2 marked out.png


Cyl 1 WPS.psdata
(1.49 MiB) Downloaded 66 times


This second capture is one I didn't originally intend to do but because of results I initially got. It had to be done. It's taken from inside the exhaust manifold. About 15 cm's after the exhaust valve but before it joins cyl 4 output. The configuration of this exhaust is cyl 1 and 4 combine in the manifold and cyl's 3 and 2 also combine. These two separate 'ports' then connect to two separate engine pipes. After around 75 cm the two pipes combine to form one pipe. Followed by a cat, an extremely large muffler then just before the tail pipe, a second muffler.

image 02.1.png



image 2.1.png


FLS Crank Ex manifold.psdata
(1.66 MiB) Downloaded 64 times


Straight away we can see their is a very sudden drop off of exhaust pressure. To confirm exactly how much this pressure drop is I have redone the test with WPS. The result, to me, was surprising. Not what I expected. A lot more vacuum than expected.

Image 03.1.png


Image 3.1.png


WPS Crank Ex manifold.psdata
(1.69 MiB) Downloaded 56 times


We can see the biggest drops are by cyl 1 and cyl 4 as expected. And surprisingly we can see how much 2 and 3 effect the FLS considering how far the points are separated and half the journey is against flow of the exhaust gas.
Now we know what happens and when inside the cylinder and just outside the exhaust valve so if we combine all the info from the above captures, we can see how it all ties together

Image 6.1.png


Combined capture.psdata
(3.2 MiB) Downloaded 58 times


It has to be said. Yes, we can see overlap. At least there is reasonable evidence to say we can, after all the images don't line up perfectly but because of the varying conditions, it's going to be hard to. If you don't except that as overlap it's time to stop reading and if that's not it, it definitely can't be seen. But that drop actually makes a significant difference in exhaust pressure - nearly 0.4 psi. So where is it?
I'm going to show you how to find it - first time every time. At least on a C20SEL engine. That I'm going to do in the next post as this is becoming an epilogue. :shock:
But one last thing to note is the scaling in each capture. I would have preferred to keep it the same all the way through this fantastic journey but it effected the capture to much. You will see what I mean.

Cheers
FF
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Re: The search for overlap.

Postby Fat Freddy » Tue Apr 28, 2015 7:47 am

So it looks like overlap does at least make it into the exhaust manifold. So where does it end up? I wanted to know because I have seen many examples of people claiming a certain feature of a waveform is caused by overlap or a valve opening/closing etc.. Even last week an ex technician told me about an awesome tool he had seen at a technical show in Melbourne that could find overlap :roll: .

So I have followed it. Right through the system. To make it easy I have done a few images. The first are using the homemade FLS and the second lot are with the WPS measuring actual pressure change. Even though the FLS is home made it is consistent and what it displays matches with what the WPS shows.

In each image I have used reference waveforms of different position through the exhaust, so to see where the overlap moves to. Each reference was done at a very close RPM. It was then delayed ='ve or -'ve along with a secondary ignition sync to align it with the crank sensor in the image. So .......

Blue - Exhaust manifold about 15 Cm from number 1 Exhaust valve.
Black - In the 1/4 Engine pipe 25 Cm from previous test.
Lime - Just after where the exhaust becomes a singular pipe 52 Cm from previous test point.
Magenta - Between Cat and first muffler 82 Cm from previous test point.
Grey - After first muffler 123 Cm from previous test point.
Cyan - At tail pipe after second muffler 160 Cm from previous test point.

Also in these first images the scaling has been changed to show the change that occurs through the exhaust.

FLS not scaled.png
FLS through exhaust


With this captures of the WPS the displayed pressure is slightly delayed (approx. 4ms) because of the filtering occurring within the WPS device it's self.

WPS not scaled.png
Actual pressure change through exhaust.


On these second images the scaling is done as if all measurements were done at the same voltage/psi. This shows how much actual change has actually occurred.

FLS kept scale.png
FLS as if voltage scale had not been changed.


WPS kept scale.png
WPS as if voltage scale had not been changed.


What has happened to the overlap reminds me of a hole in the sand and the side's have caved in. You can see the epicentre but the detail of the sides has gone. But you can still estimate where the side was or where the exhaust valve closed.
What have I achieved from this? Weather I'm right or wrong I will no longer be staring at exhaust captures wondering how to figure out where certain events are. I can see, at least for a C20SEL where overlap epicentre occurred. I also know that feature , lumps and dips come and go. The cat seems to remove a lot of detail but the centre muffler appears to add??? I hope someone takes this and proves it wrong.

FLS.png


FLS.psdata
(5.31 MiB) Downloaded 54 times


WPS.psdata
(5.63 MiB) Downloaded 52 times


Hopefully I have here the actual files. The position of the rulers are where the images have been taken.

At the end of the day I can see the exhaust is doing exactly as intended. It's removing energy/noise/heat. But I don't need no $400 tool to see overlap. My hand does just fine. :wink:

The end.

Cheers
FF
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Re: The search for overlap.

Postby Steve Smith » Fri May 08, 2015 9:52 am

Hello FF and THANK YOU.

If I had a hat I would take if off in respect not just "tip it"

Can you first of all apologise to your wife who no doubt has put up with you drilling holes in her exhaust system, then staring at your PC for hours on end.(no doubt into the early hours)

Once again this is such a rare insight into the activity throughout an exhaust that no doubt will differ from vehicle to vehicle, but highlights characteristics that will be present with all.

I was amazed by the results obtained just 15 cm away from the exhaust valve producing a vacuum which I could not have envisaged until now

A bone of contention when discussing exhaust gas pulsations is the time delay from combustion to exit at the tailpipe.

This can play havoc when attempting to identify an offending cylinder.

Thanks to the relentless hard work, persistence and patience you have applied here, I can see on this vehicle we have approx. 24 ms delay and this would be the first evidence (to my knowledge) that I have seen presenting hard facts that we can share with users around the world...thank you.

I will speak to Mike here at Pico (our Technical Author) as I would like to see your hard work and research exposed as much as possible.

Not sure where in the world you are but if our paths should cross, the beers are on me.

Take care......Steve
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Re: The search for overlap.

Postby Autonerdz » Sat May 09, 2015 1:17 am

steve smith wrote:
A bone of contention when discussing exhaust gas pulsations is the time delay from combustion to exit at the tailpipe.



We have had that conversation on our forums.

Consider the speed of sound and how long that really would take to travel the length of the exhaust system.. :wink:
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Re: The search for overlap.

Postby Alan » Mon May 11, 2015 7:26 am

Autonerdz wrote:
steve smith wrote:
A bone of contention when discussing exhaust gas pulsations is the time delay from combustion to exit at the tailpipe.



We have had that conversation on our forums.

Consider the speed of sound and how long that really would take to travel the length of the exhaust system.. :wink:


Which is about 340 meters / second (or about 3 milliseconds per meter) - a number you can prove using your PicoScope and a balloon :D
https://www.picotech.com/library/experi ... d-of-sound
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Re: The search for overlap.

Postby hexibot43 » Mon May 11, 2015 5:24 pm

FF,

Well done. I wish I had the free time you do. My wife would have been finding me Honey-dewS after a 1/2 hour. I must admit to still be digesting all that I've seen. I'm thinking to myself how am I going to easily put this to use? But I am not dis-believing anymore. Elusive but really there.

Thanks,

MAB
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Re: The search for overlap.

Postby Fat Freddy » Sun May 17, 2015 10:15 am

Thanks Steve.

Can you first of all apologise to your wife who no doubt has put up with you drilling holes in her exhaust system, then staring at your PC for hours on end.(no doubt into the early hours)

Once again this is such a rare insight into the activity throughout an exhaust that no doubt will differ from vehicle to vehicle, but highlights characteristics that will be present with all.

I was amazed by the results obtained just 15 cm away from the exhaust valve producing a vacuum which I could not have envisaged until now



You aren't wrong Steve, many, many hours went into this :D but not as many that went into trying to figure out how to spot where the overlap was evident. And I do enjoy questioning what some may consider the written word.( Not that I'm necessarily correct either - just my observation.) Even now I'm still finding more observations in the captures. But now we know just how much a pressure wave is bastardised through the exhaust by different components found in almost every exhaust system.
The vacuum in the produced also blew me away as well. It was one of the reasons I had to go a lot deeper into this than first expected (I actually hadn't confirmed it until after I started this thread). And have since come across an article that measured the vacuum in the port it's self at multiple Psi. So I may have a crack at confirming that too.

This can play havoc when attempting to identify an offending cylinder.

Thanks to the relentless hard work, persistence and patience you have applied here, I can see on this vehicle we have approx. 24 ms delay and this would be the first evidence (to my knowledge) that I have seen presenting hard facts that we can share with users around the world...thank you


You have to see what a misfire does :wink: :twisted: . I didn't post that because I felt it derailed what I was after too much.
I concur, 24ms is what I measure also. I was surprised how much it varied through out the system. And I hope it does give others something to think about. Even an opposing argument. It keeps everybody on their toes. :)

Not sure where in the world you are but if our paths should cross, the beers are on me.


Done!!! I'll see ya down Bondi. A schooner of Tooheys New for me.

Chink! Chink!
FF
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Re: The search for overlap.

Postby Fat Freddy » Sun May 17, 2015 10:19 am

Autonerdz wrote:
steve smith wrote:
A bone of contention when discussing exhaust gas pulsations is the time delay from combustion to exit at the tailpipe.



We have had that conversation on our forums.

Consider the speed of sound and how long that really would take to travel the length of the exhaust system.. :wink:


Hi Tom, Alan.

I may have to investigate the speed through. I personally doubt it's anywhere near the speed of sound. I agree with Steve's measurement of about 24 ms . - Challenge excepted. :shock:

The speed of sound in an exhaust system would have to be at it's slowest point probably 350 M sec to over 550 M sec in the manifold. I suspect the varying pressure's of the medium (I suspect that is what you are referring to Tom) it's travelling through is some what slower.
On this exhaust that's (give or take) 10 milliseconds. The pressure drops are 6 ms at there narrowest. That cover's a lot of exhaust at the speed of sound.

I have a couple of idea's about tackling this. One of the question's I want to know is the pressure drop from 3 & 2 in the manifold for the exhaust of 1 & 4. Did it reflect back up the engine pipe against the gas flow? Did I miss something in the manifold it's self? Even though this engine has no EGR valve, casting's in the head are there for it. Are all the ports connected with in the head? :shock:

Measuring pulse speed with minimal variations shouldn't be to hard. One of the problems I did have was variation of engine RPM to try and keep all matched. I also noticed the 'pocket' depth would vary. In hind sight I should of disconnected the Oxygen sensor as I could hear :evil: what seemed to be fuel control. Although I haven't confirmed this occurring . (And for anyone who hasn't heard an Oxygen sensor control fuelling, scope and listen - easy at about 2000RPM) .

Cheers
FF
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Re: The search for overlap.

Postby Fat Freddy » Sun May 17, 2015 10:25 am

hexibot43 wrote:FF,

Well done. I wish I had the free time you do. My wife would have been finding me Honey-dewS after a 1/2 hour. I must admit to still be digesting all that I've seen. I'm thinking to myself how am I going to easily put this to use? But I am not dis-believing anymore. Elusive but really there.

Thanks,

MAB


Thanks Hex.

I didn't get leave that easily. Had to wait for the minister (war and finance) to have projects of her own involving the kids before I got a crack at this. Hence the time it has taken to execute this thread.
Personally I'm still not convinced there is a lot of detail that could be pulled from an exhaust waveform. But I did not expect what I considered to be non existent at the tail pipe to become 50% of the wave. Albeit, totally obliterated.

But thanks for watching. And the feed back is much appreciated. :)

Cheers
FF
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Re: The search for overlap.

Postby KimAndersen » Sun May 17, 2015 2:44 pm

Hi FF

Interesting subject you have brought up here.

I must admit that I have not read this subject that deeply, but one thing there caught my eyes when I was reading your last post, was your talk about the speed in the exhaust system.

Just to refresh you, remember that the speed of sound depends on the exhaust gas temperature.

I found this link http://www.qrg.northwestern.edu/projects/vss/docs/propulsion/3-how-you-calculate-specific-impulse.html that might interest you and other technical minded persons. :wink:

Regards
Kim
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